Pulmonary barotrauma (PBT) of ascent is the most serious of the barotraumas, and it causes concern in all types of diving operations. It is a clinical manifestation of Boyle’s Law because it affects the lungs and results from overdistension and rupture of the pulmonary tissue by expanding gases during ascent. It can occur in compressed air divers, submariners undertaking escape ascent training, hyperbaric patients during decompression and airline passengers during ascent to altitude (though the last two situations are rare and invariably associated with gas-trapping disease in the lung).
A 1988 review1 of submarine escape training from 11 nations showed that despite careful selection procedures and extremely high standards of training and supervision, hooded buoyant ascent (in which the trainees head is enclosed by a hood providing a breathable air space) had an incident rate for PBT between 0.1 and 0.6 per 1000 escapes and a fatality rate 10 to 50 times lower than that. In non-hooded ascents (in which the trainee must breathe out continually during the ascent), the incident range was 1 to 19 per 1000 escapes. The incidence in recreational diving is unknown.